Conventional ocular zoom lenses are described, for example, in Japanese Patent No. H7-34061 and Japanese Laid Open Patent Application H9-251131. These zoom lenses are composed of, in order from the eye-point side, a first lens group of positive refractive power that is formed of a cemented lens, a second lens group of positive refractive power that is formed of a single lens element, and a third lens group of negative refractive power that is formed of a cemented lens. The second and third lens groups are moved along the optical axis in opposite directions for zooming.
The above-described zoom lenses ensure a relatively large eye relief (i.e., the distance from the lens surface that is the nearest the eye point to the eye point) and provide relatively satisfactory correction of aberrations. However, the image angle at low magnifications is approximately 40xc2x0, which is too small.
The present invention relates to an ocular zoom lens that may be used, for example, with a telescope as well as with binoculars. The object of the present invention is to provide an ocular zoom lens that ensures sufficient eye relief using a relatively small number of lens elements while satisfactorily correcting aberrations, even for wide image angles.